The present invention relates to laser beam technology, and in particular, to an apparatus for combining the laser beams from two separate lasers to provide an output laser beam having a power which is approximately the sum of each of the individual laser beams. In particular, the invention avoids the difficulties encountered in a folded cavity laser, and especially misalignment problems which occur during movement of such folded cavity lasers, i.e., in surgical laser systems, for example.
The present surgical laser technology, particularly for carbon dioxide lasers, requires cavity folding when power in excess of 60 or 70 watts is required. This is true of both flowing gas and sealed lasers.
With the technique known as cavity folding, two gain sections are connected in a series arrangement. The laser beam from the first gain section is folded into a second gain section with a total output beam power from the second gain section of approximately the combined power of both individual sections. The problem with this technique is that the two gain sections and accessory optical components, such as mirrors for folding the laser beams, must be very accurately aligned. If the laser beam from the first gain section is misaligned as it impinges on the second gain section, the individual sections may stop lasing altogether and no output will result.
Without the use of folding, if a single laser is used, the laser cavity will become impossibly long to package in an ergonomic manner.
Experience teaches that folded lasers never remain as well aligned as single pass lasers since there are between one and two additional mirrors and mounts in the resonant cavity as well as beam tubes, all of which must be mechanically very stable with respect to a common reference, the frame of the laser. The more mirror mounts and frame members, i.e., tubes, supports and braces, the more accumulated angular mirror motion that results due to temperature changes, relief of stresses over time and movement. This seriously impairs cavity resonance and reduces output power and mode quality.
Applicant is aware of the following references which relate to the laser art:
4,649,351- Veldkamp et al 4,220,928- Bloom et al PA1 4,550,240- Toida et al 4,364,014- Gray PA1 4,573,465- Sugiyama et al 3,950,707- Hill et al PA1 4,672,969- Dew 4,396,284- Presta, et al
U.S. Pat. No. 4,649,351 to Veldkamp et al describes an apparatus and method for coherently adding laser beams. The patent discloses an apparatus provided for summing a plurality of lasers coherently by phase locking the plurality of lasers and by diffracting a plurality of beams into a single beam. A defraction grating is utilized having a configuration to generate upon illumination substantially equal intensities of diffraction orders corresponding to the number of lasers while suppressing higher unwanted orders. Phase locking is accomplished by a single master laser, or by a cavity mirror to generate reference beams. The output beams of the plurality of lasers are coherently superimposed by the grating.
U.S. Pat. No. 4,550,240 to Toida et al discloses a laser irradiating apparatus comprising a first laser source for outputting a first laser beam and a second laser source for outputting a second laser beam. The laser beams are selectively irradiated through either a first light guide or a second light guide. A first laser beam and a second laser beam are combined by mixing means comprising a plurality of mirrors and a dichroic mirror which transmits the light from the first laser beam and reflects the light from the second laser beam.
U.S. Pat. No. 4,573,465 to Sugiyama et al shows an apparatus where two laser sources are combined using a dichroic mirror, similar to the Toida et al reference. The laser irradiation apparatus of the Sugiyama et al patent irradiates a plurality of working laser beams having different wavelengths to obtain complex effects in medical treatment.
U.S. Pat. No. 4,672,969 to Dew discloses a laser healing method in which the laser beams from a first laser and an auxiliary laser are provided to an area of medical treatment by optical elements.
U.S. Pat. No. 4,396,285 to Presta et al discloses a laser system for medical applications having two lasers and a movable concave reflector. The lasers are capable of generating beams of coherent electromagnetic radiation. One of the beams, an aiming beam, is aligned to impinge the reflector, to reflect therefrom and to impinge a biological specimen. The reflector is moved until the beam is aligned to impinge the desired position. The reflector is held stationary and the second beam is generated. The second beam is also aligned to impinge the reflector to reflect therefrom and to impinge the same desired position as that impinged by the first beam. This reference shows a conventional type of structure in which the first beam is used for aiming or guiding purposes and the second laser beam is utilized for the actual treatment.